Apparatus for growth of large crystals in gels

ABSTRACT

AN APPARATUS FOR GROWING SINGLE CRYSTALS OF A RELATIVELY LARGE SIZE HAVING FIRST AND SECOND REACTANT CONTAINING RESERVOIRS RESPECTIVELY POSSESSING RELATIVELY LARGE VOLUMES IN RELATION TO THE VOLUME OF A CRYSTAL GROWING CHAMBER POSITIONED IN A HORIZONTAL RELATIONSHIP BETWEEN THE RESERVOIRS AND INTERCONNECTED THERETO. CRYSTAL GROWTH IS EFFECTED IN A GEL MATRIX POSITIONED WITHIN THE CRYSTAL GROWING CHAMBER WITH THE FIRST AND SECOND RESERVOIRS CONTAINING THE REQUIRED CRYSTAL GROWING SOLUTIONS NEEDED TO BRING ABOUT CRYSTAL GROWTH.

May 11., ARM|NGTON ETAL APPARATUS FOR GROWTH OF LARGE CRYSTALS IN GELSFiled Oct. 24, 1967 5% m 1, m W W V7 A 40 m MM 5 0 E United StatesPatent O "ice 3,578,414 APPARATUS FOR GROWTH OF LARGE CRYSTALS IN GELSAlton F. Armington, Lexington, and John J. OConnor, Arlington, Mass.,assignors to the United States of America as represented by theSecretary of the All Force Filed Oct. 24, 1967, Ser. No. 677,791

Int. Cl. B01d 9/02 U.S. Cl. 23-273 3 Claims ABSTRACT OF THE DISCLOSUREAn apparatus for growing single crystals of a relatively large sizehaving first and second reactant containing reservoirs respectivelypossessing relatively large volumes in relation to the volume of acrystal growing chamber positioned in a horizontal relationship betweenthe reservoirs and interconnected thereto. Crystal growth is effected ina gel matrix positioned within the crystal growing chamber with thefirst and second reservoirs containing the required crystal growingsolutions needed to bring about crystal growth.

BACKGROUND OF THE INVENTION This invention relates to an apparatus forgrowing electromagnetic crystals at room temperature. More particularly,this invention concerns itself with an apparatus for growing largesingle crystals within a gel matrix which comprises large reactantmaterial storage reservoirs positioned on both sides of andinterconnected to a crystal growing chamber containing the gel matrix.

The increased use of single crystals in a variety of electronicapplications has created a need for the development of crystallinematerials that possess an overall high quality and the requisiteelectromagnetic characteristics. In general, crystal growing techniquesinvolve the use of elevated temperatures and high vacuums. One systemoften employed to effect the growth of crystalline materials such ascuprous chloride, cuprous bromide, silver chloride, lead sulfide andother well-known electromagnetic crystals is the melt method whichutilizes extremely high temperatures. The use of high temperatures,however, often produces defective crystals. The presence of a phasetransi' tion below the melting point of the material often producesstress and strain faults within the crystal structure. The stress andstrain faults are also further intensified by various temperaturegradients during the period of cooling to room temperature.Contamination from container materials also constitutes another seriousdisadvantage when using the melt method to effect crystalline growth.

To overcome the problems and disadvantages inherent with the use ofelevated temperature conditions, it has been found that single crystalscan be grown within a gel matrix. The method, in general, involves thegeneration of a chemical reaction within the gel matrix between twosoluble reactant materials to form an insoluable reaction product. Theplacing of a chemically complexed crystalline containing solution incontact with a gel matrix is another method which has proved to befeasible for producing high quality single crystals. The chemicalcomplexing agent diffuses through the gel at a faster rate than thedesired crystalline containing material. The crystalline containingmaterial is rendered insoluble by dilution and precipitates out assingle crystals. Although this latter method of using complexing agentshas proved effective in growing high quality crystals, it has notproduced crystals of a size large enough for use in certainapplications.

3,578,414 Patented May 11, 1971 The lack of uniform concentrationgradients and the problem of maintaining stationary concentrationgradients within the gel matrix appears to be responsible for the growthof the relatively small size crystals obtained heretofore.

SUMMARY OF THE INVENTION In accordance with the present invention, ithas been found that relatively large single crystals, free of defectsand of an overall high quality can be formed within a gel matrix byutilizing an apparatus comprising a first and second reactant containingreservoir means which possess a large volume area. The reservoir meansare positioned on each side of a crystal growing chamber and areinterconnected therewith. The volumetric ratio between the individualreservoirs and the crystal growing chamber is at least greater than 10to 1. The large volumetric ratio is needed to prevent the creation ofnonuniform concentration gradients within the gel matrix contained inthe chamber.

The apparatus of the invention provides a simple and economical meansfor growing large single crystals of a uniform diameter at roomtemperatures and ambient pressures without resorting to the complexcontrol problems encountered in high temperature crystal growingmethods.

Accordingly, the primary object of this invention is to provide anapparatus for growing large single crystals at room temperature.

Another object of this invention is to provide an apparatus for growingelectromagnetic crystals within a gel matrix.

Still another object of this invention is to provide an apparatus thatis particularly adapted for controlling the concentration gradients ofcrystal growing solutions within a gel matrix.

A further object of this invention is to provide an ap paratus forgrowing single crystals within a gel matrix that allows a uniform andstationary concentration gradient to be set up in the gel matrix.

Still a further object of this invention is to provide an apparatuswhich allows for the growth of electromagnetic single crystals of largesize in a simple and economical manner.

The above and still further objects, advantages and features of thisinvention will become apparent upon consideration of the followingdetailed description thereof taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, the figures representillustrative embodiments of the invention:

FIG. 1 is a front elevational view of one embodiment of the inventionillustrating its various elements.

FIGS. 2., 3 and 4 are front elevational views of additional embodimentsof the apparatus of this invention; and

FIG. 5 is an enlarged front elevational view of a portion of theapparatus disclosed in FIG. 1.

In all the figures, like elements are represented by like numerals.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there isshown a first reservoir 10 for supplying a rectant material to a crystalgrowing chamber 12. A second reservoir 14 is positioned in a horizontalrelationship to the chamber 12 in the same manner as reservoir 10.Reservoirs 10 and 14 are interconnected respectively to chamber 12 bymeans of conduits 16, 18, 20 and 22. The crystal growing chamber 12 isin the convenient form of a U-tube and contains a gel matrix 24.

The large reservoirs L and 14 are positioned on both sides of thechamber 12in a horizontal relationship rather than in a verticalrelationship over the gel in order to minimize pressure on the gel 24,particularly when filling the reservoirs with crystal growing solutions.A volumetric ratio between the individual volumes of reservoirs 10 and1-4 and the volume of the crystal growing chamber of greater than 10 to11 is necessary in order to effectuate crystal growth. Volumetric ratiosin the range of about 15 to 1 are preferred. Larger ratios may beemployed, but do not contribute to the effectiveness of crystal growth.The use of the large reservoirs allows a uniform concentration gradientto be set up and maintained in a stationary manner within the gel matrix24 of the chamber 12. Thus, since the crystals form at specificconcentrations and the concentration gradient is stationary in thisapparatus, large crystals can be formed at the location where the properconcentration is present.

The apparatus of FIG. 1 has been successfuly employed for the formationof cuprous chloride crystals within a gel matrix by the dilution of asaturated cuprous chloride solution complexed in hydrochloric acid. Thefollowing detailed example is presented to illustrate the operation ofthe apparatus disclosed herein.

Example A silica gel 24 is first prepared by titrating l N hydrochloricacid with 0.5 molar sodium metasilicate to a pH of about 5. The gel 24is poured into the U-tube shaped chamber 12 up to a level immediatelybelow the conduits 18 and 22 and allowed to settle. After 24 hours, oneliter of a saturated cuprous chloride chemically complexed solution 34is placed in reservoir 10. The saturated solution 134 is complexed bysaturating a 5 N hydrochloricacid solution with cuprous chloride. Oneliter of distilled water 36 is placed in reservoir 14. The solutions 34and 36 are covered with a layer of parafiin oil, not shown, to reduceoxidation. After two weeks, crystals 38 begin to form in the gel 24within the crystal growing chamber 12 as more clearly shown by referringto FIG. 5. Within one month, the crystals were still clear and were 6mm. or larger. The largest clear crystals are 6 mm. on an edge while thelargest clear crystals that could be produced by 4 and are employed toadd structural stability to the apparatus. The double conduits 16, 18,20' and 22 of FIG. v1 are utilized for mechanical stability andstructural strength and either the double or single connecting conduitsof FIGS. 1 and 2 are suitable.

FIG. 3 represents a further embodiment in which the crystal growingchamber 12 lies in a horizontal, centrally disposed relationship ratherthan the U-shaped form of FIGS. 1, 2 and 5. All the embodimentsrepresented by FIGS. 1, 2, 3 and 5 are vented to the atmosphere andrequire the addition of a parafin oil to the surface of the reactantsolutions to prevent oxidation. FIG. 4, however, illustrates a closedsystem in which the reservoirs 10 and 14 are connected by means ofclamps 30 and 32. In this embodiment, the utilization of a paraffin oilis not needed to prevent oxidation.

The apparatus of this invention has proved to be most effective inproducing large single electromagnetic crystals in a simple andeconomical manner. Large crystals of cuprous chloride have been producedby the apparatus of this invention and find particular use as modularsfor larity in reference to specific embodiments thereof, it is to beclearly understood that the disclosure of the present invention is forthe purpose of illustration only and is not intended to limit theinvention in any way, the scope of which is defined by the appendedclaims.

What is claimed is:

1. An apparatus for growing single crystals within a gel matrixcomprising, a first reservoir having a predetermined volume for thestorage of a reactant material, a second reservoir having apredetermined volume for the storage of a reactant material, said firstand second reservoirs being laterally spaced and disposed in ahorizontal relationship, a crystal growing chamber of a size to allowfor crystal growth positioned between said first and second reservoirsand operatively connected thereto to permit the establishment of astationary, uniform reactant a conventional gel growth method were 3 mm.This rep resents an eight-fold increase in crystal volume.

Two factors that limit the ultimate crystal size in the usual gel growthmethods are the depletion of the reactants and the increase inby-product concentration as the crystal grows. The apparatus of thisinvention reduces both of these factors. The volume of the reservoir 10containing cuprous chloride is so large that the cuprous chlorideconcentration is not significantly decreased by removal of the cuprouschloride into the silica gel 24. The volume of the water reservoir 14 isso large that the hydrochloric acid liberated when the cuprous chloridecrystals 38 are formed does not significantly increase the acidity ofthe water reservoir. Thus, in this apparatus, the concentration ofhydrochloric acid and cuprous chloride along the length of the gelapproaches a steady state condition because of the essentially constantconcentrations at the gel interfaces. When this steady state is nearlyreached, there will exist sites along the length of the gel whereconditions are favorable for crystal growth and will remain favorablefor a relatively long period of time. This steady state is not attainedwhen crystals are grown by conventional techniques. If one tries to growlarge crystals of cuprous chloride in a test-tube, the advancing acidfront tends to dissolve crystals that have already been formed.

FIG. 2 represents a different embodiment of the apparatus of thisinvention showing the two reservoirs 10 and 14 interconnectedrespectively to chamber 112 by means of single conduits 26 and .218. Thesingle conduits of FIG. 2 are of a larger diameter than the conduits ofFIG. 1

concentration gradient within said growing chamber, said growing chamberhaving a predetermined volume for the storage of a gel matrix in whichthe ratio of the predetermined volume of the growing chamber to each ofthe predetermined volumes of the first and second reservoirs is lessthan 1 to 10 and a gel matrix stored within said chamber.

2. An apparatus in accordance with claim 1 in which each of the firstand second reservoirs are sealed from the atmosphere to preventevaporation and oxidation of the reactant materials.

3. An apparatus in accordance with claim 1 in which the crystal growingchamber forms a U-shaped tube and the gel matrix is disposed within thelower portion of the U-shaped tube and positioned below the horizontallevel of the said operative connection.

References Cited UNITED STATES PATENTS 1,850,499 3/1932 Francis 23-2922,014,823 9/1935 Tramm 23-292 2,532,257 11/1950 Kirshenbaum et al. 232923,371,036 2/1968 Torgesen et al. 2330l OTHER REFERENCES Modern Lab.Appliances, Fisher Scientific Co., p. 392 (1952 Central Scientific Co.Catalog #H351 (1935), p. 571.

NORMAN YUDKOFF, Primary Examiner R. T. FOSTER, Assistant Examiner U.S.Cl. X.R. 23-295, 300

